1. Field of the Invention
The present invention relates generally to liquid fluid loss control additives for oil field cements, and more particularly, to liquid fluid loss control additives which can be stored and then efficiently combined with a cement slurry or the water to be used for forming the slurry.
2. Description of the Prior Art
In cementing operations carried out in oil, gas and water wells, a hydraulic cement is normally mixed with sufficient water to form a pumpable slurry and the slurry is pumped into a subterranean zone to be cemented by way of the well bore penetrating such zone. After placement in the zone, the cement slurry sets into a hard mass.
Certain hydrophilic water soluble polymers have long been recognized by those skilled in the art of oil field cementing as cement additives useful in reducing fluid loss from cement slurries to surrounding subterranean formations as the slurries are being placed or after placement and prior to setting. It is desirable to include fluid loss additives in oil field cements for various reasons. In primary cementing, where a cement slurry is placed in the annulus between a casing or liner and the well bore to seal the annulus and bond the casing or liner to adjacent earth formations, loss of fluid to the formations can result in premature gelation of the cement slurry and bridging of the annulus before proper placement of the slurry. In remedial cementing operations, the control of fluid loss is necessary to achieve the more precise cement slurry placement associated with such operations.
The hydrophilic water soluble polymers commonly utilized as fluid loss agents in cement slurries are solids and have in the past required elaborate mixing apparatus and techniques. That is, when dry powdered hydrophilic polymers are contacted with water in which they are being mixed, unless particular care and special mixing techniques and apparatus are utilized, agglomerated particles form masses referred to as gel balls and/or fish eyes which are difficult to break up and dissolve in the water. These problems as well as the special mixing apparatus and techniques are obviated when the hydrophilic fluid loss control polymers are combined with cement slurries or the water used to form the slurries in the form of liquid additives.
Various liquid fluid loss control additives for oil field cements have been developed heretofore. However, they generally have been difficult to handle because of their high viscosity and have contained relatively low concentrations of hydrophilic fluid loss control polymers making their use expensive. Several liquid fluid loss control additives have been developed wherein the hydrophilic polymer or polymers are suspended in water insoluble organic liquids along with surfactants and thickeners. These liquid additives often suffer from excessive settling when stored and the settled materials develop extremely high viscosities making such materials very difficult to resuspend in the additive.
U.S. Pat. No. 4,435,217 issued Mar. 6, 1984 discloses concentrated hydrophilic polymer suspensions having improved thermal aging stability. That is, in accordance with the patent, liquid polymer suspensions formed with organic liquids are provided with improved resistance to settling and the development of high viscosity settled materials by the addition of liquid fatty acids to the suspensions.
By the present invention, hydrocarbon base liquid fluid loss control additives for oil field cements are provided which contain high concentrations of fluid loss control polymers, which obviate the mixing and settling problems mentioned above and which are efficient and inexpensive to use.